1. Field of the Invention
The invention relates in general to a voltage regulation device with a Zener diode, and more particularly to a voltage regulation device, which has a Zener diode and can save power loss.
2. Description of the Related Art
FIG. 1A is a circuit diagram showing a conventional voltage regulation device with a Zener diode. An enabling signal EN is used to enable a voltage regulation device 100. A timing signal generating unit 102 is driven by the enabling signal EN to generate a timing signal CLK, and a charge pump 104 increases a voltage level of an output voltage Vout to drive a loading device 110 according to the timing signal CLK.
FIG. 1B shows a curve of the current with respect to the voltage of the Zener diode 106 of FIG. 1A. As shown in FIG. 1B, when the Zener diode 106 is operating in a breakdown region, it has a special voltage-to-current characteristic curve. In this case, no matter how the current Iz flowing through the Zener diode 106 is, a crossover voltage across two ends of the Zener diode 106 is substantially equal to a breakdown voltage Vz1 of the Zener diode 106 such that the output voltage Vout is substantially equal to the breakdown voltage Vz1 and the voltage regulating effect may be achieved. However, the conventional voltage regulation device 100 has several drawbacks.
The voltage regulation device 100 cannot terminate the operation of the charge pump 104 when the output voltage Vout reaches a predetermined voltage level. The charge pump 104 continuously operates to increase the voltage level of the output voltage Vout and to generate an output current flowing through the Zener diode 106 to the grounding level. Thus, the voltage regulation device 100 disadvantageously has the higher power consumption and the lower power efficiency. Besides, the output voltage Vout of Zener diode 106 varies as its temperature varies, since the temperature coefficient of the Zener diode 106 is not zero. The temperature coefficient of the Zener diode may be, for example, positive. Thus, the output voltage Vout of the regulation device 100 disadvantageously varies with the temperature.
FIG. 1C shows a circuit diagram of a conventional voltage regulation device with operational amplifier. Voltage regulation device 10 enables a transistor Tx for lifting the voltage level of an output voltage Vo2 through the output voltage Vo1 of the operational amplifier OP1. The voltage regulation device 10 further provides the output voltage Vo2 to the inverting input terminal of the operational amplifier OP1 in a signal feedback manner, for disabling the transistor Tx and pulling down the voltage level of the output voltage Vo2 through current source 112 when the voltage of the output voltage Vo2 is higher than a voltage V1. Such that, the output voltage Vo2 is regulated through the negative feedback manner. However, the conventional voltage regulation device 10 must use the operational amplifier OP1 to regulate the output voltage Vo2. Such that, the conventional voltage regulation device disadvantageously has high circuit complexity and high cost.